1. Field of the Invention
The invention, in general relates to a novel method and apparatus for producing samples of primarily finely granulated and dry material and, more particularly, to a method and apparatus for producing samples of pulverized combustion residue such as, for example, filter and fly ash, for defining their residual carbon content by defining changes in electrical parameters of a complex electrical component which includes the produced samples of primarily finely granulated and dry material to be examined.
The invention is intended especially for use in ash collection sites of furnaces in coal-fired power plants. In this connection, reference is made primarily to fly ash without, however, intending thus to limit the field of application of the invention. For the invention is advantageously applicable wherever residual carbon contents of mainly finely granulated and dry material is to be defined by defining changes in electrical parameters of complex electrical components which contain the material to be examined. In addition to furnaces of power plants this may also be incinerators and cement making plants.
Defining residual carbon contents of fly ash is necessary, on the one hand, for controlling and optimizing the combustion process, i.e., for use of as much of the energy as is contained in the fuel. On the other hand, defining residual carbon content is necessary for controlling the quality of fly ash to be used as an additive in building materials and cement. Under both aspects, the invention aims at providing as low a residual carbon content, or as low a proportion of uncombusted components, as possible. Changing load conditions in a firing plant and different fuel compounds require constant monitoring of the combustion process which, in turn, leads to the requirement of continuously defining the residual carbon content or periodically to define it in short intervals of time or with no or very little time lag.
2. Statement of the Prior Art
At present, the method employed by power plants is to draw samples followed by an analytic examination of the samples in a laboratory. This is expensive and results in such significant losses of time that for all intents and purposes it is impossible to optimize the combustion process.
For that reason efforts have not been wanting to develop methods and apparatus which make it possible to define residual carbon content in a simple manner, continuously or periodically, without any loss of time. In this connection, those methods have been found to be particularly suitable which are based upon a change in the electrical parameters of complex electric components which contain the fly ash to be measured. However, the handling of fly ash is extremely difficult because of its extremely complicated bulk behavior.
German Laid-Open Patent Specification No. DE-OS 33 03 177 disclosed a method and an apparatus for measuring the carbon content of fly ash in which the capacity of a capacitor is evaluated into which a sample of fly ash is introduced as a dielectric substance. Fly ash is removed from a silo by means of a feed screw and is transmitted to a measuring chamber which constitutes the nonconductor of the capacitor, and is compacted by vibration. Thereafter, the capacity of the measuring chamber containing the compacted fly ash is defined. After defining the capacity the fly ash is removed from the measuring chamber and returned to the silo by a different feed screw. The carbon content of the fly ash is deduced from the measured capacity. The method may be practiced continually or periodically, but in order to obtain useful measuring values care has to be taken in ensuring that the mean quantity of fly ash contained in the measuring chamber is substantially constant and of defined density.
A basically comparable solution has been described in German laid-open patent application No. 198 56 870. In this case, ash transported by a pneumatic feed system is fed to a sampler, care being taken to realize a predetermined particle content of the probe by way of exhaust filters and light barrier. The sample is heated to a predetermined analyzing temperature and is compacted by a shaking device. Thereafter it is subjected to a microwave analyzer. Microwave resonance techniques are used as is well known to define the residual carbon content of the prepared sample fed to the microwave analyzer. Once it has been examined, the sample is returned to the feed system.
Either method require rather complex apparatus for the withdrawal, preparation and return of the sample. The complexity is last not least owing to the extremely poor bulk behavior of the fly ash to be tested. Moreover, the attained precision of the residual carbon content has been found to be unsatisfactory. More particularly, the attained measuring values tend to be vastly scattered. Accordingly, they can only be conditionally used for controlling combustion processes.